Abstract

This report describes a probabilistic assessment methodology developed by the
U.S. Geological Survey (USGS) for evaluation of the resource potential for storage of
carbon dioxide (CO2) in the subsurface of the United States as authorized by the
Energy Independence and Security Act (Public Law 110–140, 2007). The methodology is
based on USGS assessment methodologies for oil and gas resources created and refined
over the last 30 years. The resource that is evaluated is the volume of pore space in
the subsurface in the depth range of 3,000 to 13,000 feet that can be described within
a geologically defined storage assessment unit consisting of a storage formation and
an enclosing seal formation.

Storage assessment units are divided into physical traps (PTs), which in most cases
are oil and gas reservoirs, and the surrounding saline formation (SF), which encompasses
the remainder of the storage formation. The storage resource is determined separately for
these two types of storage. Monte Carlo simulation methods are used to calculate a
distribution of the potential storage size for individual PTs and the SF. To estimate
the aggregate storage resource of all PTs, a second Monte Carlo simulation step is used
to sample the size and number of PTs. The probability of successful storage for individual
PTs or the entire SF, defined in this methodology by the likelihood that the amount of
CO2 stored will be greater than a prescribed minimum, is based on an estimate
of the probability of containment using present-day geologic knowledge. The report
concludes with a brief discussion of needed research data that could be used to
refine assessment methodologies for CO2 sequestration.